1. Field of the Invention
The invention relates to a journal bearing for the shafts of high-speed rotors.
2. Discussion of Background
Large axial and radial forces act on high-speed rotors, such as the shafts of turbochargers, and these forces are accepted by appropriately configured and arranged thrust bearings and journal bearings. In addition, it is also necessary to provide compensation for the radial rotor vibrations if troublefree operation is to be ensured. For this purpose, so-called squeeze film dampers which reduce the amplitude of the rotor vibrations occurring are employed in turbomachines. Such a squeeze film damper consists essentially of an annular gap configured between a bearing sleeve and a bearing housing and connected to an oil supply. Because the bearing sleeve is also supported by a hydrodynamic lubricating film on the shaft side, it is often also referred to as a floating sleeve. In the case of nonrotating floating sleeves, the problem arises--particularly in the case of heavy rotors--that the floating sleeve is not centered during operation. It is, rather, positioned in the lower region of the bore which accommodates it. This leads, on the one hand, to poorer damping properties and, on the other, to wear of the corresponding components.
Numerous possibilities for centering a squeeze film damper are known to avoid these disadvantages (see article "Application of Squeeze Film Dampers", by F. Y. Zeidan, in Turbomachinery International, September/October 1995, p. 51, FIG. 2-4). These are O-ring centering arrangements in the axial region of the squeeze film damper, centering being by means of a lateral spring rod cage and by means of leaf springs arranged radially and locally at the periphery. A further squeeze film damper centering arrangement by means of bending rods arranged radially at the outside is known from the article "Linear Force Coefficients for Squeeze-Film Dampers", by A. Z. Seri et al in Transactions of the ASME, p. 326, Vol. 105, July 1983.
A disadvantageous feature of O-ring centering, however, is that this has a nonlinear spring characteristic and unsatisfactory long-term behavior whereas, in the case of the spring rod cage, a very large amount of axial installation space is necessary. On the other hand, the bending rods require a large amount of radial space and, because of the large number of individual parts, involve high costs and unsatisfactory concentricity accuracy. The leaf spring solution, which likewise requires a large amount of radial space, can only be manufactured by the electrical discharge machining method. In this case, furthermore, there is danger of shaft-side deformation of the bearing sleeve.
Wear-free centering elements for centrifugal machines with a vertical shaft arrangement have been known, as such, for a long time (U.S. Pat. No. 3,950,964) but have not been employed up to now for the centering of squeeze film dampers and have not been used in the case of turbomachines and their high-speed rotors.